This invention relates to an automotive windshield fog sensor. More particularly, this invention relates to an integrated glass fog sensor unit terminated on a flex circuit.
Windshield fog conditions are predicated on windshield surface temperature, ambient air temperature and ambient humidity within the occupant compartment. Dew-point is calculated from the ambient air temperature and ambient humidity. An indicator of fog entails the relationship of this dew-point with the windshield surface temperature.
A common instance of fogging occurs when a vehicle is initially cold prior to people entering. With people entering the vehicle compartment, the ambient air temperature and humidity increase. The windshield surface temperature remains cold and the air film about the surface is also cold. Since cold air can not contain as much moisture as warm air, it separates out and settles, in a liquid phase, on the cold windshield surface. Once the phase change occurs, from vapor to liquid, changing the liquid back to vapor takes a long time due to additional energy requirements necessary to achieve a phase change. For this reason, it is desirable to predict fogging before it occurs. Typical infrared fog sensing technology is capable of detecting the presence of fog, but not predicting fog before it occurs.
Instrumentation exists which can measure surface temperature, air temperature and air humidity, and if properly applied, can predict fogging on an automotive windshield as disclosed in U.S. Pat. No. 5,701,752 granted to Masaru Tsunokawa, Yukikatsu Ozaki, Chiryu Onimaru, and Takahisa Suzuki, Dec. 30, 1997.
The sensors required to predict fogging are typically placed individually within the vicinity of a glass surface, such as the vehicle compartment of a windshield. This placement often requires separate wire harnesses. The ambient air sensors are placed at a safe distance away from the windshield so that the cold glass surface does not interfere with the ambient air readings. That is, free space, or air, is typically relied on to provide the necessary thermal barrier between the glass surface temperature sensor and the ambient air sensors.
Accordingly, the present invention relates to an integrated glass fog sensor unit which serves to provide the necessary data to a fog control unit, such as that integrated into the heating, ventilation, and air conditioning control system, HVAC, of a vehicle. The unit is secured to an interior glass surface of a windshield by way of a tray having an adhesive layer backing. The unit has an ambient air temperature sensor, an ambient humidity sensor and a glass temperature sensor. The electrical connections are made by using a flex circuit. The ambient air temperature sensor is directly adjacent to the humidity sensor. The tray and the flex circuit also serve as a thermal barrier isolating the ambient air sensor and humidity sensor from the potentially cold glass surface. The glass temperature sensor sits within a hole, penetrating the tray and the flex circuit, so that the sensor is in direct contact with the glass surface. All three sensors are located beneath a protective dome which is secured to a perimeter wall of the tray.
The flex circuit has a conductor sensor end which conforms to the shape of a perimeter wall of the tray. This shape serves to limit movement of the flex circuit conductor sensor end thereby holding the sensors steady. The sensors are positioned to share a common ground.
Thus, an advantage of the present invention is a single fog sensor unit which is made possible by a combination of the tray and the flex circuit functioning as a thermal barrier, thereby reducing manufacturing costs.
Another advantage of the present invention is simplification of wiring by use of a common ground made possible by the centralization of the sensors necessary to predict fogging conditions, thereby reducing manufacturing costs.
Yet another advantage of the present invention is the use and shape of the flex circuit which conforms to the perimeter wall of the tray, thereby providing a simple, inexpensive, means to secure the flex circuit to the unit.